In general, a well-known hot air generating heater, which conducts heating by means of electricity, is used for supplying hot air to a processing device. However, the hot air generating heater uses a large amount of power because the hot air generating heater is used in such a manner that the hot air generating heater increases a temperature of gas directly from a room temperature to a desired temperature by resistance heating or induction heating of the gas. Further, starting-up of the hot air generating heater is not stable, because the heating to a target hot-air temperature is affected by a temperature of the gas to be heated.
A possible solution to the former problem is to use a heat pump, as in a clothes drying device as described in Patent Literature 1. The heat pump has been in widespread use in recent years due to its recognized ability to save energy as compared to direct heating. However, the use of the heat pump has a difficulty in attaining stable temperature control.
In this respect, Patent Literature 1 discloses that a temperature control is carried out by valving a flow path for CO2 (cooling medium).
However, there is a concern that pressure of CO2 may almost reach a pressure of 100 atm, because the CO2 cooling medium in a supercritical state is used. Because of this, employing the mechanical control as described above in the processing device for a work ironically results in increased costs and also has a risk of a device failure, unless the mechanical control is employed in a large individual device such as the clothes drying device.
Further, stability at the time of start-up is not improved even in the case of using the heat pump, because the performance is affected by such a factor as a change in temperature of a low temperature-side heat source.
Still further, precise temperature setting is not easy in the heat pump. Therefore, the heat pump cannot be used for hot air supply for processing a work, the processing requiring strict temperature setting. Such processing that requires strict temperature setting is, for example, pre-molding drying of a metal hoop for use in insert molding for manufacturing an electronic component.